Extreme Programming (XP) is a software development approach for small teams on risk-prone projects with unstable requirements. Testing ('extreme testing') is a core aspect of Extreme Programming. Programmers are expected to write unit and functional test code first - before writing the application code. Test code is under source control along with the rest of the code. Customers are expected to be an integral part of the project team and to help develope scenarios for acceptance/black box testing. Acceptance tests are preferably automated, and are modified and rerun for each of the frequent development iterations. QA and test personnel are also required to be an integral part of the project team. Detailed requirements documentation is not used, and frequent re-scheduling, re-estimating, and re-prioritizing is expected. For more info on XP and other 'agile' software development approaches (Scrum, Crystal, etc.) see resource listings in the Softwareqatest.com 'Other Resources' section.